chris N, Eisenhower was not going to send troops to Hungary and couldn't without first invading Austria as well so any recognition/ultimatum from the US is only going to have the result of the Eisenhower administration being humiliated before the entire planet and right before the US election.
The Soviets are not going to permit a breach in the Warsaw Pact, even before considering the precedent it would have set for Poland and there is no credible evidence that the Soviets would have acted differently, least of all unidentified books coming out generations after the fact.
Dementor, except that outside the Soviet bloc Vietnam was never able to get any nation at the UN to support that claim. And the regime they established consisted of nothing but Khmer Rouge members in every position of authority, which didn't help their claims.